Convertible contact structure for an electromagnetically operated switch



March 17, 1970 w, sg ua l c; ETAL 3,501,717 CONVERTIBLE CONTACT STRUCTURE FOR AN ELECTROMAGNETICALLY OPERATED SWITCH Filed Sept. 12, 1968 W alliF 6 INVENTOR. ALLIN W. SCHUBRING 64 KENNETH L. PAAPE United States Patent 3,501,717 CONVERTIBLE CONTACT STRUCTURE FOR AN ELECTROMAGNETICALLY OPERATED SWITCH Allin W. Schubring, Milwaukee, and Kenneth L. Paape, Mequon, Wis., assignors to Square D Company, Park Ridge, Ill., a corporation of Michigan Filed Sept. 12, 1968, Ser. No. 759,382

Int. Cl. H01h 73/12 US. Cl. 33517 Claims ABSTRACT OF THE DISCLOSURE An arrangement for achieving conversion of the contacts from normally open to normally closed contact operation in a relay having a readily removable front contact and terminal which when removed will provide access and permit rotation of a movable contact about its support and wherein both the stationary front contact and the support carry portions indicating the operating condition of the contacts.

This invention relates to electric circuit controlling devices and more particularly, to electromagnetic control devices having contacts which may be readily converted to accommodate the requirements of a control system.

Electric control circuits for solenoids, motors and the like, wherein devices known as relays are employed, .present a variety of circuit conditions and therefore it is mos: desirable that the relays used therein have contact structures that may be arranged and converted for normally open or normally closed contact operation and vice versa. Further, it is desirable that the conversion be accomplished with minimum difliculty when the conversion is attempted at a workbench, as well as when the relay is mounted on a panel, and the circuit controlled by the relay requires modification.

Additionally, it is desirable that suitable designations be provided on the relay structure so that inspection of the relay will readily indicate the operating condition of the relay contacts whereby wiring of the relays during installation may be more readily accomplished without error. In the present invention, the conversion from normally closed to normally open contact operation or vice versa, is alfected simply by temporarily removing one of the stationary contacts at the front of the relay, rotating the bridging contact about a support and restoring the removed contact in a position wherein an instruction carried on the stationary contact corresponds to an instruction carried on the movable contact supporting structure.

It is an object of the present invention to provide an electric circuit controlling device with contact structures which may be readily converted to provide the device with a normally open and a normally closed contact operation and to provide suitable designations on the movable and one of the stationary contact structures of the device to indicate the operating condition of the contacts.

An additional object is to provide an electric current controlling device with movable and stationary contact structures which are labeled to indicate the type of operation which the contacts will provide.

A further object is to provide an electric current controlling device, such as a relay, with contact structures 'which may be readily converted to provide the relay with normally open or closed contacts and wherein one of the stationary contacts is removably mounted in an opening in a front wall of a support to provide access to a movable contact in a chamber of the support so the movable contact may be rotated from one position to another position in the chamber to convert the relay from a normally closed to a normally open type of contact oper- 3,501,717 Patented Mar. 17, 1970 Ice ation and vice versa, without disassembly of the remaining components of the relay.

A further object is to provide an electric current controlling device, such as a relay, with contact structures which may be readily converted to provide the relay with normally open or closed contacts and wherein one of the stationary contacts is removably mounted in an opening in a front wall of a support to provide access to a movable contact in a chamber of the support so the movable contact may be rotated from one position to another position in the chamber to convert the relay from a normally closed to a normally open type of contact operation and vice versa without disassembly of the remaining components of the relay and to provide suitable indicia on the movable contact structure and the removable stationary contact structure which will indicate the type of operation the contacts will provide.

Further objects and features of the invention will be readily apparent to those skilled in the art from the specification and appended drawing illustrating a preferred embodiment in which:

FIG. 1 is a front view in elevation of an electromagnetic switch including a convertible contact structure according to the present invention.

FIG. 2 is a side view of the switch in FIG. 1 with a portion thereof shown in cross section as taken along line 2.2 in FIG. 1.

' FIG. 3 is a view in cross section of the contact structures of the switch in FIG. 1 showing the contacts in a normally closed position.

FIG. 4 is an exploded view in perspective showing the stationary contact structure detached from remaining components of the switch in FIG. 1.

FIGS. 5, 6, 7 and 8 are plan views of components used in the movable contact assembly in FIGS. 2 and 3.

FIG. 9 is a cross sectional view of a support for a stationary contact as used in the switch in FIG. 1.

The electric circuit controlling device or switch 10, shown in the drawing, includes a base 12, preferably formed as a unitary part of die cast metal material to have a set of openings 14 for mounting the switch 10 on a vertical panel, not shown, with an electromagnet assembly 16 positioned at the lower vertical portion of the base 12. The opening 14 at the top of the base 12 is an inverted keyhole shaped opening and the pair of openings 14 at the bottom of the base are slots having exposed ends at the bottom edge of the base 12.. The structure of the base 12, the electromagnet 16, the arrangement for mounting the electromagnet 16 on the base 12 and structure for causing linear reciprocable movement of a contact carrier 18 is fully disclosed and described in an application for United. States Patent Ser. No. 759,381, which is concurrently filed herewith and has been assigned by the inventor Kenneth J. Marien to the assignee of the present invention.

An insulating support 20 is secured at a top portion of the 'base 12 by a pair of screws 22. The base 12 is symmetrical about a vertical centerline 24 and includes at its upper portion a suitable ledge 26 and slots to receive nuts 30 which receive the screws 22. and secure the insulating support 20 to the base 12. The base 12 additionally has a stop wall 32 extending outwardly at a loca tion below the ledge 26. The stop wall 32 limits the movement of the contact carrier 18 in a downward direction.

The insulating support 20 is preferably formed of a suitable molded material to have a plurality of spaced parallel partitions 34 extending forwardly of a rear wall 36 and downwardly of a top wall 38 to define a plurality of chambers 40 which are identical and spaced from each other in the insulating support 20'. The partitions 34 extend forwardly of the rear wall 3-6 and downwardly of the top wall 38 so each of the chambers 40 has an open front end 42 and an open bottom end 44, as defined by the front and bottom edges of the partitions 34. Extending downwardly into each chamber 40 from the top wall 38 are bosses, each of which provide a downwardly facing stop surface 46 that is spaced from the top wall 38. Extending between adjacent partitions 34 at the open front end 42 of each chamber 40 is a mounting portion 48 for a stationary contact assembly 50. The mounting portions 48 bridge partitions 34 and partly close the open front ends 42 and the open bottom end 44 of each chamber 40. As shown in FIG. 9, each mounting portion 48 has a hexagonal cross sectional shape having a slot 52 therein. The hexagonal shape of each mounting portion 48 provides: front and rear surfaces 54 and 55 that extend parallel to the rear wall 36, a Set of parallel surfaces 56 and 57, respectively, facing upwardly and downwardly at the front and rear portions of the mounting portion 48 and a set of parallel surfaces 58 and 59 respectively facing upwardly and downwardly at the rear and the front portions of the mounting portion 48.'The slot 52 which extends completely through the front surface 54 and the surfaces 56 and 59 and partly into the surfaces 57 and 58, provides clearance for the passageof a securing screw 60 of the stationary contact assembly 50.

The contact carrier 18 also is formed of a molded insulating material to have a portion 62 at its lower end attached so as to be moved upwardly by an armature 64 of the electromagnet 16 when a coil 66 of the electromagnet 16 is energized and a pair of arms 68 guided by the base 12 and portions of the electromagnet assembly 16. The arms 68 are connected to a bar-like portion 70 that is positioned to move between the stop wall 32 and the insulating support 20. Extending upwardly from the bar-like portion 70 are a plurality of identical spaced frames 72 equal in number to the number of chambers 40 in the insulating support 20. The frames 72 are moved vertically by the electromagnet 16 along an axis 74 that is spaced between the open front end 42 and the rear wall 36. As shown in FIG. 8, each of the frames 72 includes a pair of walls 76 upstanding from the bar-like portion 70, a crossbar portion 78 interconnecting the upper free ends of the walls 76, and a bottom surface 80 that is formed on the bar-like portion 70. Extending upwardly from the bottom surface 80 between the rear edges of the walls 76 is a stop ledge 82. The crossbar portions 78 each have an upper surface 84, a lower surface 86 and undercut portions 88 extending upwardly in the bottom surfaces 86 adjacent the walls 76. The walls 76, the crossbar portions 78 and the surface 80 of the frames 72 thus define a space 90.

Each of the frames 72 is provided with a movable contact assembly 92 that includes an elongated contact finger 94 and a means for supporting the contact finger on either the upper surface 84 or the lower surface 86 of the crossbar portion 7 8 and to permit the contact finger 94 to be rotatably moved about the crossbar portion 78. The means for mounting the contact finger 94 on the crossbar portion 78 includes a dual sling-like member 96, a spring seat 98 and a compression spring 100.

The sling-like member 96 is mounted for rotary movement on the crossbar 78 so it may be moved to either of two selected positions and is formed of a unitary metal part which has a pair of parallel spaced support portions 102 resting adjacent the walls 76 ends on the cross bar 78. Additionally, the sling-like member 96 has a pair of supported portions 104 and 105 spaced from the crossbar 78 when the sling-like member is in either of its two positions and two pairs of arms 106 interconnecting the supported portions 104 and 105 with the support portions 102. The support portions 102 are spaced from each other and similarly, the supported portions 104 and 105 are spaced from each other in a manner that when the pair of supported portions 104 and 105 are passed over the crossbar portion 78, the support portions 102 will engage the material of the crossbar portions 78 provided by the undereut portions 88. After the sling-like member 96 is thus positioned on the crossbar portion 78, the spring seat 98 is attached to the pair of supported portions 104 and to close the space therebetween. The spring seat 98 preferably is formed of a molded material, such as nylon, which is relatively rigid and still capable of being flered to permit its installation on the supported portions 104. As shown in FIG. 5, the supported portion 104 has an outwardly extending edge 110 and an inwardly extendingnotch 112. Similarly, the supported portion 105 has an outwardly extending edge 114 With a tang 116 projecting therefrom and an inwardly extending notch 118. The notch 118 has a greater width than the notch 112. The spring seat, which is shown in an enlarged view in FIG. 6, includes a stop surface 120, a Spring seat surface 122, an end 124 which receives the supported portion 104 and an end 126 which receives the supported portion 105. The spring seat surface 122 has a circular boss 128 formed thereon which receives the convolutions of the spring 100 to position one end of the spring 100 on the spring seat 98. The ends 124 and 126, respectively, have lip portions extending to provide hook portions 130 and 132 which face in the same direction. The hook portion 132 includes a portion 134 having a Width greater than the notch 112 and receivable in the notch 118 together with the tang 116 prevents incorrect installation of the spring seat 98 on the supported portions 104 and 105. The hook portion 130 has an inclined latch portion 136 thereon which is receivable in the notch 112. The ends 124 and 126, respectively, have surfaces 138 and 140 thereon. The surfaces 138 and 140 extend parallel to each other and each includes an indicia that is observable from the open front end 42 of the insulating support 20 when the movable contact assembly 92 is positioned on the crossbar portion 78. As shown, the surface 138 includes the letters NO, indicating normally open contacts, and the surface 140 includes the letters NC, indicating normally closed contacts. The cr ssbar portion 78 is provided with a rib, not shown, which has a width greater than the width of the notch 112 and capable of being received in the notch 118. Thus the sling-like member 96 is prevented from incorrect installation on the crossbar portion 78. As previously disclosed, the spring seat 98 may be installed only to face in one direction on the supported portions 104 and 105. Thus, after the sling-like member 96 is correctly positioned on the crossbar portion 78 and the spring seat 98 is correctly installed on the portions by aligning the hooks 130 and 132 respectively with the supported portions 104 and 105 and moving the spring seat 98 across the supported portions 104 and 105 to a position wherein the hooks 130 and 132 embrace the supported portions 104 and 105, the latch 136 which is received in the notch 112 prevents dissassembly of the spring seat 98 from the supported portions 104 and 105.

The movable contact finger 94 includes a medial portion 142 and a pair of contact portions 144 and 146 on opposite sides of the medial portion adjacent opposite ends of the finger 94. The medial portion as shown in FIG. 7 is provided with a centrally raised portion 148 which serves as a spring seat for an end of the spring 100 and notches 150 which are received by the pairs of arms 106 to position and guide the contact finger 94 for movement along the pair of arms 106. The contact finger 94 is installed by inserting the finger 94 between the spring seat 98 and the cross bar portion 78 to a position wherein the notches 150 receive the two pairs of arms 106 and the spring seat 148 faces the boss 128. After the contact finger 94 is thus positioned, the spring 100 is positioned to have its opposite ends resting on the boss 128 and the raised portion 148 to constantly urge the medial portion 142 into engagement with either the upper 84 or lower 86 surfaces of the crossbar 78, as will be later described. Also, as shown, the spring seat 98 has notches 151 formed therein at spaced locations which will accept the tip of a screwdriver or other suitable tool for the purpose of aiding the rotation of the contact finger 94 about the crossbar 78. When the contact finger 94 is positioned on the crossbar 78, it will have its contact portions 144 and 146 on opposite sides of the axis 74.

A stationary contact assembly 152, which is included in each chamber 40, has an upwardly facing contact portion 154 and a downwardly facing contact portion 156 positioned within the chamber 40 at a position between the axis 74 and the rear wall 36 to be selectively engaged by the contact portions 144 or 146 when the movable contact assembly 92 is at either of its two positions on the crossbar 78. The contact portions 154 and 156 are carried on an end of a conductive member that has a portion 158 positioned adjacent the rear wall 36, and portion 160 positioned adjacent the top wall 38 that extends through an opening in the top wall 38 to a terminal portion 162 which is exposed externally of the insulating support 20 and includes a threaded opening which receives a screw 164 and supports a wire clamp 166 as are used to connect the relay in a circuit. The stationary contact assembly 152 is positioned in the chamber 40 against removal by a screw 167 which extends through a bore in the top wall 38 and is received in a threaded opening in the portion 160. While not specifically shown, the terminal portion 160 is suitably slotted to receive the boss carrying the stop surface 46.

The stationary contact assembly 50 provided for each chamber 40 includes a mounting portion 168 which may be removably secured in either of two positions on the mounting portion 48 to position a contact portion 170 within the chamber 40 so that'it will be disposed between the axis 74 and the open front end 42 in a position to be engaged by the contact portions 144 or 146. The stationary contact assembly 50 additionally includes a wire connecting portion 172 and an indicating portion 174. The mounting portion 168 includes a threaded opening that receives the screw 60 and is arranged to be positioned on either of the surfaces 58 or 57.

The stationary contact assembly 50 may be mounted in either of two positions on the mounting portion 48. When the stationary contact assembly 50 is mounted on the support 48, as shown in FIG. 2, the mounting portion 168 will rest upon the mounting surface 58 and the head of the screw will be tightened against the surface 59 as the shank of the screw extends through the slot 52 and is threaded into the opening in the mounting portion 168. When the stationary contact assembly 50 is positioned as shown in FIG. 2, the wire connecting portion 172. will point downwardly and the indicating portion 174 which is formed as a pointed extension on the wire connecting portion 172 will point downwardly. When the electromagnet 16 is de-energized and the movable contact assembly is positioned on the crossbar 78, as shown in FIG. 2, the spring seat 98 will rest on the surface 80 and the contact finger 94 will be positioned on the crossbar 78 so that the contact surfaces 144 and 146 face upwardly and are separated from and in a position to engage the contact surfaces 170 and 156. In this connection it is to be noted that the shape of the stationary contact assembly 50 is arranged to position the contact surface 170 in a plane common with the contact surface 156 when the stationary contact assembly 50 is positioned as in FIG. 2. When the electromagnet is de-energized, a spring 176 reacting between the base 12 and the contact carrier 18 causes the contact carrier 18 to be moved downwardly to a position wherein the bar portion 70 engages the stop wall 32 and the contact surfaces 144 and 146 are separated from the contact portions 170 and 156, permitting the spring 100 to position the medial portion 142 of the contact finger 94 on the lower surface 86 of the crossbar 7 8. When the electromagnet 16 is energized, the contact carrier 18 is moved upwardly against the force of the spring 176 to a position wherein the contact surfaces 144 and 146 engage the contact surfaces 170 and 156. After the movable contacts engage the stationary contacts, the motion of the contactcarrier 18 continues and the movable contact finger 94 moves out of engagementwith the surface 86 along the arms 106 of the sling-like member 96 against the force of the spring 100 which compresses the spring 100 which in turn forces the contact surfaces 144 and 146 into tight engagement with the contact surfaces 170 and 156.

When the electromagnet 16 is de-energized, the spring 176 urges the carrier 18 downwardly to position the parts of the device as shown in FIG. 2. It will be seen that when the components of the device are positioned as shown in FIG. 2, the surface 138 bearing the indicia NO will be visible through the open front end 42 as shown in FIG. 1. Further, when the stationary contact assembly 50 is positioned to provide the NO contact operation, the portion 174 will point toward the surface 138 bearing the indicia NO to advise that the contacts of the relay are 1n a normally open contact position.

When it is required to convert the contacts of the relay from a normally open to a normally closed contact operation, shown in FIG. 3, the screw 60 is loosened from its position in the mounting portion 168 and the entire stationary contact assembly 50 is removed from its position on the mounting portion 48. The slot 52in the mounting portion 48 permits the removal of the stationary contact assembly 50 to be readily accomplished. After the stationary contact assembly 50 is detached from the switch 10, access to the movable contact assembly 92 is provided through the open front end 42. The absence of the contact surface 170, because of the detached stationary contact assembly 50, will permit the rotation of the movable contact assembly 92 in a clockwise direction about the crossbar 78. The rotation of the movable contact assembly 92 is accomplished by inserting a suitable tool, such as a screwdriver, through the open front end 42 into the notches 151 to cause rotation of the contact finger 94 and the sling-like member 96 to the position shown in FIG. 3, wherein the stop surface engagesthe stop surface 46 and the contact fingers 94 is separated from the upper surface 84 of the crossbar 78. After the movable contact assembly 92 is positioned as shown in FIG. 3, the contact assembly 50 is installed on the support 20 by inverting the contact assembly 50 from the position shown in FIG. 2 to the position shown In FIG. 3 and inserting the contact assembly 50 through the open front end 42 into the chamber 40 to a position wherein the mounting portion 168 rests upon the surface 57. When the screw 60 is tightened, the head of the screw 60 will engage the surface 56 and maintain the contact assembly 50 on the mounting portion 48 with the contact surface facing upwardly and aligned in a plane normal to the axis 74 with the contact surface 154. When the contact surfaces 170 and 154 are thus positioned, they are respectively engaged by the contact surfaces 146 and 144 when the electromagnet 16 is de-energized. When the movable contact assembly 92 is positioned as shown in FIG. 3, the spring seat 98 will engage the stop surface 46 and the contact finger 94 will be separated from the crossbar 78. Thus when the electromagnet 16 is energized and the contact carrier 18 is moved upwardly against the force of the spring 176, the crossbar 78 will move into engagement with the contact finger 94 and force the contact finger 94 upwardly against the force of the spring 100 to a position wherein the contact surfaces 146 and 144 are respectively separated from the contact surfaces 170 and 154. When the electromagnet 16 is deenergized, the contact carrier 18 is moved downwardly by the force of the spring 176. The downward movement of the contact carrier 18 permits the spring 100 to move the contact finger 94 downwardly to a position wherein the contact surfaces 146 and 144 on the contact finger 94 engage the contact surfaces 170 and 154. When the contact carrier is in its f-urthest downward position the contact finger 94 is separated from the crossbar 78 and the spring 100 maintains a firm seating engagement between the movable contacts 144 and 146 and the stationary contact surfaces 154 and 170.

When the stationary contact assembly 50 and the movable contact assembly 92 are positioned as shown in FIG. 3, the surface 140 bearing the indicia NC will be visible through the open front end 42 and the indicating portion 174 on the stationary contact assembly 50 will point upwardly, as shown in FIG. 3, indicating that the contacts Within the chamber 40 are in the normally closed condition of operation.

When it is desired to convert the contacts from the position shown in FIG. 3 to the position shown in FIG. 2, the stationary contact assembly 50 is detached from the switch as previously described and the movable contact assembly 92 is rotated about the crossbar 7 8 in a counterclockwise direction by a suitable tool which is inserted through the open front end 42 to the position shown in FIG. 2. The rotation in the counterclockwise direction is facilitated by the tang 116 which will be engaged by the tip of the screwdriver and the notches 151 in the spring seat 98. When the movable contact assembly 92 is positioned as shown in FIG. 2, the stop surface 120' will rest upon the surface 80 and the assembly will be prevented from movinging in a counterclockwise direction beyond the position shown in FIG. 2 by the engagement between the surface 140 and the stop ledge 82 so that the movable contact assembly will be positioned so that its surface 138 bearing the indicia NO, or normally open contacts, is closely visible through the open front end 42 of the switch 10.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

1. In an electric circuit controlling device, the combination comprising: an insulating support providing a chamber having an open front end, an open bottom end and a rear wall, an insulating linearly reciprocable contact carrier including a cross bar portion movable in the chamber along an axis that is spaced between the front end and the rear wall, an elongated contact finger having a pair of contact portions thereon respectively adjacent opposite ends thereof, means mounting the contact finger on the crossbar for rotary movement thereabout to either of two selected positions wherein the contact finger presents a contact portion of each side of the axis, a first stationary contact assembly having a contact portion positioned within the chamber for engagement with a contact portion on the contact finger at the side of the axis between the axis and the rear wall, a second stationary contact assembly having a mounting portion removably secured on the insulating support and a contact portion positioned within the chamber for engagement with a contact portion on the contact finger at the side of the axis between the axis and the open front end, said means for mounting the contact finger on the crossbar including a sling-like member mounted for rotary movement about the crossbar to either of two selected positions, said member having a pair of parallel spaced support portions resting on the cross bar, a pair of parallel spaced supported portions spaced from the cross bar and two pairs of arms interconnecting the supported and the support portions, a spring seat immovably mounted on and interconnecting the supported portions so the spring seat is spaced from the crossbar portions, and a compression spring positioned between the spring seat and a medial portion of the contact finger and constantly urging the contact finger toward the crossbar, said spring seat being accessible through the open front end of the insulating support subsequent to the detachment of the second stationary contact assembly from the insulating support for rotatably moving the contact finger and the means for mounting the contact finger to either of the two selected positions on the crossbar.

2. In an electric circuit controlling device, the combination comprising: an insulating support providing a chamber having an open front end, an open bottom and a rear wall, an insulating linearly reciprocable contact carrier including a crossbar portion movable in the chamber along an axis that is spaced between the rear wall and the open front end, an elongated contact finger having a medial portion and a pair of contact portions thereon respectively adjacent opposite ends thereof, means for mounting the contact finger including a dual slinglike member rotatably mounted on the crossbar, a spring support mounted on the sling-like member, a spring positioned between the spring support and the medial portion of the contact finger for resiliently mounting the contact finger for rotary movement in one direction of rotation from a first position to a second position on the crossbar for converting the operation of the circuit controlling device from a normally open to a normally closed contact operation and in a direction opposite the said one direction of rotation from the second position to the first position for converting the operation of the device from the normally closed contact operation to the normally open contact operation, indicia on the spring support visible through the open front end indicating the position of the finger to provide the normally open and the normally closed contact operation of the device, a first stationary contact assembly having contact portions positioned for engagement with the contact portion on the contact finger at the side of the axis between the axis and the rear wall when the finger is at either the first and the second positions, and a secondary stationary contact assembly including a mounting portion and a contact portion, the mounting portion and the contact portion of the second stationary contact assembly being constructed and arranged so the mounting portion is removably securable in either of two invertible positions on the insulating support and the contact portion is positioned to face in either of two opposite directions for engagement with the contact portion on the contact finger at the side of the axis between the axis and open front end when the finger is at either the first and the second positions, and an indicating portion located on the mounting portion of the second stationary contact assembly to be visible from the front opening side of the insulating support to indicate the direction in which the second stationary contact portion is facing, said open front end providing access to the spring support subsequent to the removal of the second stationary contact assembly from the device for converting the device to provide the normally open and the normally closed operation.

3. The combination as recited in claim 1 wherein the mounting portion of the second stationary contact assembly is removably securable on the insulating support in either of two inverted positions.

4. The combination as recited in claim 3 wherein the mounting portion of the second stationary contact assembly includes a portion indicating the mounted position of mounting portion.

5. The combination as recited in claim 1 wherein the spring seat includes a pair of spaced faces each carrying an indicating message and located on the spring seat so that the message on one of the pair of faces is visible through the open front end when the contact finger is at one of the two selected positions and the message on the face other than the said one face is visible through the open front end when the contact finger is at a position other than the said One selected position.

6. The combination as recited in claim 5 wherein the mounting portion of the second stationary contact assembly is removably securable on the insulating support in either of two inverted positions.

7. The combination as recited in claim 6 wherein the mounting portion of the second stationary contact assembly includes a portion indicating the mounted position of mounting portion.

8. The combination as recited in claim 1 wherein the mounting portion of the second stationary contact assembly is securable in either of the two positions on a portion of the insulating support that extends between a pair of side walls of the chamber at the open front end portion of the insulating support.

9. The combination as recited in claim 8 wherein the mounting portion of the second stationary contact assembly includes a portion indicating the mounted position of mounting portion.

'10. The combination as recited in claim 9 wherein the spring seat includes a pair of spaced faces each carrying an indicating message and located on the spring seat so 15 the open front end when the contact finger is at the position other than the said one selected position.

References Cited UNITED STATES PATENTS 2,276,698 3/ 1942 Pierce. 2,897,311 7/1959 Schleicher 335-l98 2,924,685 2/ 1960 Burch. 2,985,736 5/1961 Coker 335-l98 3,243,544 3/1966 Mayer 335-198 G. HARRIS, Primary Examiner v H. BROOME, Assistant Examiner U.S. Cl. X.R.

" UNITED STATES PATENT OFFICE 569) CERTIFICATE OF CORRECTION Patent NO. 3,501,717 Dated March 17. 1970 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Co1. 3, line 10, after "bridge" insert --adJacent--.

C01. 4, line 7, for "flex-ed read --f1exed--.

C01. 5, line 63, after "electromagnet" insert 16". C01. 6, line 39, for "fingers" read --finger--.

Col. 7, line 24, for "movinging" read --moving--. C01. 8, line 33, for "secondary" road --second--.

SIGNED AND SEALED JUL 2 1970 6 .Atmt:

WILLIAM E. saflmm, JR. Edward M. Fletcher, Ir. Gomlpsloner of Paula" Attesting Officer 

